Many health organizations publish dietary and physical activity guidelines in an effort to help adults and cancer survivors make informed choices related to nutrition and physical activity. These guidelines are based on observational evidence showing that adhering to the guidelines improves breast cancer survival. Yet numerous studies have reported fewer than 30% breast cancer survivors follow the dietary and physical activity guidelines. To our knowledge, no trial has examined, in women newly diagnosed with breast cancer, the effect of adopting and practicing the dietary and physical activity guidelines on adherence to adjuvant treatments and cancer related biomarkers. We propose to examine, in 250 women newly diagnosed with Stage I-III breast cancer who are not practicing the dietary and lifestyle guidelines, and who are scheduled to receive adjuvant chemotherapy, the effect of a 1-year dietary and physical activity guidelines intervention vs. usual care on adherence to adjuvant breast cancer treatments including chemotherapy completion rates and adherence to endocrine therapy. Secondary endpoints include changes in biomarkers, body composition and quality of life. Our application is innovative and clinically meaningful as we propose to intervene soon after diagnosis when prevalence of women following the dietary and physical activity guidelines is low and likely to worsen; examine novel biomarkers and adherence to adjuvant treatments; and use a translational approach of intervening in the breast clinic and via telephone to facilitate in the eventual dissemination and implementation of our intervention. We have strong preliminary data showing a transdisciplinary team approach in recruiting breast cancer survivors into randomized lifestyle interventions during and after treatment with high adherence to the interventions. In summary, if we find our intervention improves adherence to breast cancer treatments, biomarkers and body composition, then our findings could cause a paradigm shift in how breast cancer care is delivered.